Kitchen Detective (chromatography experiment)

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Aim

The aim of the activities is to introduce chromatography as an idea to the children, but also as a way of showing them how science/chromatography can be used a tool to solve real life problems. 

This experiment was designed around KS2 / yr 3 classes. 

What you’ll need  

  • Felt tip pens with different colours (Berol or Crayola usually work well)
  • Circular filter paper 
  • Rectangles of filter paper 
  • Plastic cups
  • Water
  • Pipe cleaner (easily available from stationery/craft suppliers)

To prepare in advance 

It is good to test out the activity in advance with different felt-tips pens as some have better splitting patterns than others with different types of filter paper. Its also key for the final activity to have different makes of black pen to compare, so it’s good to test different makes of black pen too! It is useful for the final activity to have a splitting pattern of the pen used for the note left behind. The children can then compare the splitting of different pens to this one to identify the culprit. 

Activity 1: Starter exercise

To introduce the children to the idea of how chromatography works, a fun task is to let them discover what happens when the folded up filter paper is put in a slightly filled cup of water.

Instructions;

  1. Draw a shape in the centre of the filter paper. This can be any shape to start with, but symmetric shapes usually lead to more defined patterns. Also make sure the shape is not to big as this will lessen the effect. 
  2. Fold the filter paper in half 3 times (i.e. into 8ths).
  3. Add a small amount of water to a cup so that the water level is a few centremeters from the bottom of the cup. 
  4. Gently place the folded filter paper in the cup which contains the small amount of water. If the water level is to high or the placement of the filter paper too rough, the full effect will not be seen. 
  5. Once the water has climbed up the filter paper a sufficient amount (i.e. close to covering all the filter paper), remove the filter paper and unfold it. This should then reveal a pattern on the filter paper.
  6. After the first attempt, its good to let the children to be more creative with the designs in the middle of the filter paper, e.g. using multiple colours etc. But remember to make sure the shapes/drawings are not to big.  

It is good to prompt the children into observations as to what is happening. For example how the colours also move up the filter paper and how  the green will split into yellow and blue.

Activity 2: Chromatography butterflies

After making the funky patterns on the filter paper it is a fun activity for the children to make Chromatography butterflies.

Instructions;

  1. Create the pattern as before.
  2. Leave the filter paper to dry.
  3. Tie a small amount of pipe cleaner around the centre of the filter paper.
  4. Can then tie a small amount of string around the centre to hang the chromatography butterflies up!

It is good to introduce the idea of chromatography after the children have had a go with activities 1 and 2. For example describing how scientists use it to investigate what makes up a mixture in a lab or by forensic scientists to investigate clues in a crime scene through looking at the splitting pattern’s. This is also a good way of building up to the last activity. 

Activity 3: Kitchen detectives 

In the last activity, you can set the children up to solve the mystery of who stole the (insert item) and left the note behind. It is good to be creative with this to get the children interested and involved. The key behind this activity is to have felt-tip pens which give distinct splitting’s for the children to then compare using chromatography.

Setting the scene. For example someone in the staff room has stolen all the biscuits from the staff room and left a note behind – “you will never catch me”. The note was written in a pen, but who’s pen was it, Mr X or Mr Y or Ms Z? You can then say we did a test using chromatography and it gave this splitting pattern, can you use chromatography to find who’s pen matches that of the note?

Instructions;

  1. Draw a line a few centre metres above the bottom of the rectangular filter  paper (across smallest width) using 1 of the pens. 
  2. Add a small amount of water to a cup. 
  3. Gently place the filter paper in the cup. Remember it is important for this activity to make sure the water level is BELOW the line on the rectangle when the filter paper is added. If not the colours wont move up the filter paper. 
  4. Remove the filter paper just before the water has moved all the way up the filter paper. 
  5. Let the filter paper dry and then label each with a pencil of which/who’s pen was analysed.
  6. Repeat for each pen to find out who wrote the note. 
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